Aqueous base coating composition

An aqueous base coating composition comprising

• (A) a hydroxy-containing resin,
• (B) a melamine resin with a weight average molecular weight of 1,000 to 5,000, and
• (C) a diester compound represented by Formula (1)
• wherein R1 and R2 are 2-ethylpentyl, R3 is ethylene, and m is 7;
• wherein the hydroxy-containing resin (A) comprises a core-shell-type water-dispersible acrylic resin (A1′), a hydroxy-containing acrylic resin (A1) other than a core-shell-type water-dispersible acrylic resin (A1′), and a hydroxy-containing polyester resin (A2);
• the core-shell-type water-dispersible acrylic resin (A1′) comprises:
• a core copolymer (I) made by polymerizing monomers consisting of 0.1 to 30 mass % of one or more polymerizable unsaturated monomers (b) having two or more polymerizable unsaturated groups selected from the group consisting of vinyl and (meth)acryloyl per molecule, and 70 to 99.9 mass % of one or more polymerizable unsaturated monomers (c) having one polymerizable unsaturated group per molecule as monomer components;
• and
• a shell copolymer (II) made by polymerizing monomers consisting of 1 to 35 mass % of one or more hydroxy-containing polymerizable unsaturated monomers (a) having one or more polymerizable unsaturated groups selected from the group consisting of vinyl and (meth)acryloyl, 5 to 60 mass % of one or more hydrophobic polymerizable unsaturated monomers (d) having one or more polymerizable groups selected from the group consisting of vinyl and (meth)acryloyl, and 5 to 94 mass % of other polymerizable unsaturated monomer(s) (e) having one or more polymerizable unsaturated groups selected from the group consisting of vinyl and (meth)acryloyl as monomer components;
• the solids mass ratio of copolymer (I) to copolymer (II) is in the range of 10/90 to 90/10
• the proportion of the water-dispersible acrylic resin (A1′) is about 10 to about 55 mass % based on the total amount of the hydroxy-containing resin (A) and the melamine resin (B);
• the proportion of the hydroxy-containing polyester resin (A2) is about 10 to about 45 mass % based on the total mass of the hydroxy-containing resin (A) and melamine resin (B);
• and
• the proportion of the diester compound (C) in the aqueous base coating composition is about 5 to about 15 parts by mass, based on 100 parts by mass of the total of the hydroxy-containing resin (A) and the melamine resin (B);
• the one or more hydrophobic polymerizable unsaturated monomers (d) comprise one or more C6-18 alkyl-containing polymerizable unsaturated monomers and/or one or more aromatic ring-containing polymerizable unsaturated monomers.